by Karen Ward
Part III
Pressure Canning
In this part . . .
The chapters in this part explore the world of pressure canning, the canning method you use to preserve vegetables, meat, poultry, seafood, and other low-acid foods. Preserving low-acid foods requires more care than processing high-acid foods (discussed in Part II), but the rewards are well worth the additional effort. With this part, you'll safely be preserving your favorite low-acid foods in no time.
Chapter 9: Don't Blow Your Top: Pressure Canning
In This Chapter
Exploring pressure canning
Selecting a pressure canner
Understanding low-acid foods
Processing low-acid foods to perfection
Pressure canning is a process for preserving food with a low-acid content by exposing the food to a high temperature (240 degrees) under a specific pressure for a specific period of time in a specific type of pot: the pressure canner.
People who hear someone talking about pressure canning often ask, "Is it safe?" or "Won't the pressure canner explode?" These concerns are certainly valid ones, but rest assured, when you know the right way to use a pressure canner, you can safely process a variety of low-acid foods. While pressure cookers and canners of the past may have once exploded if not closed properly, the new generation of canners and cookers are much lighter in weight and have built-in safety features that release steam if the pressure gets too high. None of your grandparents' pressure cooking equipment had this.
This chapter leads you step by step through the pressure-canning process, including an explanation of pressure canning, what to look for when purchasing a pressure canner, and how to fill your canner and safely process your filled jars.
Only one form of canning — pressure canning — is approved for safely processing low-acid foods. And only one piece of equipment — a pressure canner — is approved for safely processing low-acid foods. Don't allow yourself to think you can use a substitute process or piece of equipment.
Understanding the Fuss about Low-Acid Foods
Low-acid foods contain little natural acid and require more care during the canning process than other types of foods. (If you're a techie, note that low-acid foods are foods with a pH factor — that's a measure of acidity in food — higher than 4.6.) Foods in this category include vegetables, meats, poultry, seafood, and combination foods (like soups, meat sauces, and salsas) that contain low-acid and high-acid ingredients. Exceptions to these low-acid foods sometimes include tomatoes, which are really a fruit and can be water-bath canned (although for safety's sake, you still add acid to tomatoes) and vegetables converted to high-acid foods such as sauerkraut, pickles, or pickled vegetables (discussed in Chapter 8).
Low-acid foods require pressure canning to kill microorganisms that are harmful if not destroyed before ingesting the food. Pressure canning at 240 degrees kills the botulism bacteria. If this temperature isn't achieved and the bacteria isn't destroyed, one taste of this spoiled food can kill you. And to make matters worse, these botulism-causing bacteria are odorless, have no taste, and actually thrive in low-acid foods that are in a moist environment and not in contact with air — the exact condition provided in a jar of canned food. Simply boiling food on the stovetop will not kill any botulism and should not be considered a safety step.
In a water-bath canner, the temperature of boiling water never increases above 212 degrees (the boiling point for water). While 212 degrees is fine for water-bath canning high-acid foods, it's not sufficient to safely can low-acid foods. For that, you need to superheat your filled jars to a temperature of 240 degrees, which only a pressure canner can achieve. Be sure to use a pressure canner that's approved for pressure canning by the United States Department of Agriculture (USDA).
Choosing Your Pressure Canner
A pressure canner, shown in Figure 9-1, is a heavy kettle made for processing home-canned food. It includes a locking, tight-fitting cover that makes the kettle airtight. The purpose of pressure canning is to sterilize the food by destroying hard-to-kill microorganisms, especially the bacteria that cause botulism (see Chapter 3).
Figure 9-1: A pressure canner.
Don't confuse pressure canners with pressure cookers. A pressure canner is used to process and sterilize home-canned, low-acid foods. The purpose of a pressure cooker is to cook food fast. Check out Pressure Cookers For Dummies, by Tom Lacalamita (Wiley Publishing, Inc.), for the low down on pressure cooking. Pressure canners and pressure cookers are not interchangeable. Pressure cookers are not large enough to hold the jars and the amount of water necessary to can properly. They also do not have pressure gauges that allow you to maintain the constant pressure required.
When shopping for a pressure canner, keep these things in mind:
Size: Pressure canners come in many sizes, holding from 4- to 19(!)-quart jars. For the home canner, however, a pressure canner with a capacity of 16 to 22 quarts is fine. This size holds seven 1-quart jars and permits good air circulation during processing.
Price: The cost of a pressure canner may vary from $100 on the low end to upward of $600. Some reasons for the variance are size, features, and reputation of the manufacturer.
When making your purchasing decision, study your options and estimate how frequently (or infrequently) you plan to pressure-can. You may even consider co-owning a pressure canner with a friend. If you're buying a pressure canner secondhand, take it to your local county extension office to have it checked for proper seal and be sure it's still safe to use.
Features: All pressure canners — regardless of features — safely process your filled jars of low-acid food in the same manner because a pressure canner operates in only one way. Each pressure canner has a locking cover, a pressure gauge, and an overpressure plug. Manufacturers of pressure canners, however, slightly vary the same features and add accessories in much the same way car manufacturers add extras to a basic car model.
The following sections explain the different features various pressure canners offer so that you can determine which features you prefer. The type of pressure canner you choose doesn't matter as long as the model is made and approved for processing home-canned foods.
No matter which type or size of pressure canner you choose, the goal is always the same: to superheat and process low-acid food at a high temperature (240 degrees) that destroys microorganisms.
Cover: With a gasket or without
You can find two types of covers for pressure canners: a lock-on cover and a metal-to-metal cover that's attached with wing nuts. The difference is that one has a rubber gasket to ensure an airtight seal; the other one doesn't. For a beginner, a lock-on cover is the easiest and most fail-proof to use.
Lock-on cover
A lock-on cover (see Figure 9-2) usually has a rubber gasket between the cover and the base unit to ensure to the airtight seal. To securely fasten the cover to the pressure canner, rotate the cover on the base to the locked position (matching up the handles or matching arrows or other markings on the unit) or with a type of clamping handle. To ensure that the pressure canner is properly closed, refer to your owner's manual for precise instructions.
Figure 9-2: A lock-on cover and rubber gasket.
Over time, the rubber gasket may stretch out of shape or begin to rot and deteriorate (indicated by cracking or splitting). If your gasket is in this condition, don't use your pressure canner until you've replaced the gasket. A gasket in poor condition may prevent the canner from reaching the pressure required to superheat the food and kill microorganisms.
After each use, carefully remove the gasket from the cover. Thoroughly wash the gasket in hot, soapy water and dry it well. After the gasket is completely dry, put it back on the cover so that your pressure canner is always ready for use. Some manufacturers suggest lightly coating the gasket with cooking oil, but check your owner's manual before doing this.
Metal-to-metal cover with wing nuts
A metal-to-metal cover (see Figure
9-3) doesn't require a gasket to create a tight seal; instead, this pressure canner uses wing nuts. To secure a cover with wing nuts, tighten two wing nuts on opposite sides of the canner at the same time by hand (don't use a tool and don't tighten one side at a time). Repeat this process for the remaining wing nuts.
Never tighten one nut at a time because uneven results will occur. If your wing nuts aren't tightened properly, as soon as the pressure starts to rise, water leaks out. You then have to carefully remove the canner from the heat and wait for the pressure to subside before untightening and retightening all over again.
Figure 9-3: A metal-to-metal cover with wing nuts.
Every year, check for nicks and dents in the rim of both the lid and the canner itself. These imperfections will prevent the canner from making a seal.
Gauges
Gauges are located on the top of the pressure canner cover and regulate pressure within the canner. Two types of gauges are available: a weighted gauge and a dial gauge (see Figure 9-4). A dial gauge indicates the pressure of the canner, while a weighted gauge indicates and regulates the pressure of the contents. If you're a beginner, go with the weighted gauge.
Figure 9-4: The two types of gauges available on pressure canners: A dial gauge and a weighted gauge.
Weighted gauge
A weighted gauge is simple and accurate. It's sometimes referred to as an automatic pressure control or a pressure regulator weight. This gauge allows you to cook without looking: The weighted gauge automatically controls the pressure by jiggling as the canner reaches the correct pressure. When the pressure in the canner is too high, the weighted gauge jiggles faster, and may hiss, as it releases excess steam from the canner.
A weighted gauge has a preset control that needs no service or testing to ensure an accurate pressure measurement. The pressure settings are indicated by three numbers marked on the gauge (refer to Figure 9-4): 5, 10, and 15. The numbers represent the pounds per square inch (psi) of pressure created by the trapped steam from the boiling water in the pressure canner.
The most common pressure used in pressure canning is 10 pounds, but never guess — always refer to your recipe.
Dial or steam pressure gauge
A dial or steam pressure gauge (refer to Figure 9-4) is a numbered instrument that indicates the pressure in the canner. You have to watch dial gauges carefully to be sure they don't rise too high, and you have to turn the heat up or down to keep the pressure in the right area.
Unlike the weighted gauge that requires no service, you must check this control for accuracy each season or at least once every year of use. To obtain service, refer to your owner's manual for service locations, check with the store where you purchased the canner, or contact your local cooperative extension services (see Chapter 22).
If your annual service shows that your dial gauge is off by 5 or more pounds, replace the gauge. An inaccurate reading may not produce the temperature required to kill all microorganisms. You can have your canner checked for a nominal fee, if not free, at your local hardware store or county extension office.
Vent tube, pipe vent, or petcock
Whatever the name of this feature — vent tube, pipe vent, or petcock — the function is the same (see Figure 9-5). These terms refer to an opening in the pressure-canner cover for emitting steam. Sometimes the weighted gauge sits on the vent tube.
Figure 9-5: A vent tube.
To work properly, the vent tube opening cannot be obstructed with food or other matter. Obstructions restrict the optimum pressure and temperature required for your recipe. To check the vent for obstructions, hold it up to the light. If the vent appears to be clogged, insert a piece of wire (or other item suggested in your owner's manual) into the tube. Rinse the vent with hot water. Repeat the procedure if you still see an obstruction.
Overpressure plug
An overpressure plug (see Figure 9-6) releases (pops up) if too much pressure exists in your pressure canner due to a blocked vent tube. The overpressure plug is a safety feature that's solely for your protection. If you follow the instruction manual for your pressure-canner operation, chances are this plug will never be used.
Figure 9-6: An over-pressure plug.
Rack
Your pressure canner should come with a rack. (If the rack is missing, contact the store where you made your purchase.) The perfect rack lies flat in the bottom of your canner and has lots of holes and openings that allow steam to circulate around your filled jars. Figure 9-7 is an example of a canner rack.
Figure 9-7: A rack for holding jars in the bottom of your pressure canner.
Make sure your rack is stable when you place it in the bottom of the canner. A stable rack holds jars in place, thus preventing the jars from tipping, touching other jars, or touching the sides of the canner.
A-Canning You Will Go: Instructions for Successful Pressure Canning
In order to ensure a processed product of high quality, free from microorganisms, be sure to follow each step in this section. Don't omit or modify any part. You may spend a bit more time canning low-acid foods with a pressure canner than you would canning high-acid foods in a water-bath canner, but the end result is worth the extra effort.
In this section, you begin your journey of pressure-canning low-acid foods. Avoid any temptation to omit any step or portion of any step in the process. Each step is important to produce safe, home-canned foods.
If you've never used a pressure canner before, do a trial run with no jars: Heat up the canner and go through the steps of pressurizing and depressurizing to familiarize yourself with the sounds the pressure canner makes as it builds and then releases pressure. You'll hear the steam escaping, the weight gauge shaking, and the ticking of the canner as it heats and cools; if you don't know what to expect, you could misinterpret these noises as scary or wrong.
Step 1: Gearing up
At least a couple of weeks before you want to use it, check your pressure canner and replace any gasket or missing part, have a dial gauge checked professionally, and replace a missing manual. Also count your jars and two-piece caps and examine the jars for nicks or chips, the screw bands for proper fit and corrosion, and the new lids for imperfections and scratches. It's also a good idea to select your recipe, and inventory your pantry for any nonperishable ingredients, adding any needed items to your shopping list. Your goal is to have all the supplies you need and your pressure canner in good working order on the day you're ready to can.
Preparing your pressure canner before the actual canning season means you will not find the store out of supplies and the extension agent too busy to check your gauge in time to begin canning when the produce is ripe.
On the actual canning day, get your tools ready by following these steps:
1. Assemble your prechecked equipment and utensils.
In addition to your pressure canner and the standard canning supplies (jars with two-piece lids), other items can make your canning easier: things like a food scale, extra pans for cooking your veggies and keeping a water reserve on hand, a wide-mouth funnel, and so on. Head to Chapter 2 for a list of canning supplies.
2. Wash your jars and screw bands in warm, soapy water, rinsing well to remove any soap residue.
Double-check for nicks and dents and discard any damaged items.
3. Place your clean jars and lids in a kettle of hot — not boiling — water until you're ready to fill them.
Never boil the lids because the sealant material may be damaged and won't produce a safe vacuum seal.
4. Ready your canner by filling it with 2 to 3 inches of water and heating the water.
Always read the manufacturer's instructions for your pressure canner and follow them to the letter.
Also, assemble the other canning items you need. You can find a complete list in Chapter 2.
Step 2: Preparing your food
Always start with food of the highest, freshest quality. Food that's spoiled or bruised doesn't improve in quality during the pressure-cann
ing process! To prepare your food for pressure canning, follow these steps:
1. Wash all food prior to packing it in the jars or precooking it.
For detailed instructions on washing your food, refer to Chapter 3.
2. Thoroughly cut away all evidence of spoilage or discard any inferior products.
3. Prepare the food by precisely following your recipe.
Some recipes call for you to fill your jars with raw food; others may want you to precook the food. If you're precooking your low-acid food before filling your jars, don't discard the cooking liquid; use this liquid for filling your jars.
Work in manageable batches. To determine just what a "manageable batch" is, consider how much food fills one canner load at a time. Most recipes are geared for manageable batches, but if you're in doubt, check the yield for the recipe.
Step 3: Filling your jars
Always place your product into hot jars (you keep them hot by leaving them in a kettle of hot water, as explained in the earlier section "Step 1: Gearing up.") To fill your jars, follow these steps:
1. Remove a jar from the kettle and pack the food into the jar so that the food is snug, yet loose enough for liquid to circulate into the open spaces.
2. Ladle boiling water (or the liquid from precooking the vegetables) into the jars, leaving the amount of headspace stated in your recipe.
If you're adding cooking liquid, divide the cooking liquid evenly among the jars and finish filling the jars with boiling water, if necessary. That way, if you run short of the cooking liquid, you won't have one jar filled with only boiling water.
